Commercial Propane Bulk Storage Tanks

[chicopee]

Is there any reason to do internal inspections on said tanks
having being in continuous use for 20 years? Moisture accumulation in such tanks is drastically reduced since methanol is added by transport drivers while filling such tanks.

Did anyone perform internal inspections on such tanks with at least two decades of useage? If so, what were the approximate ages of the tanks and what internal conditions did you find? Was any internal erosion of metal evident around the threaded openings to the liquid fill lines?

 

[vpl]

Isn't there an EPA standard?

Not really my field, but ran across this during a nuclear plant license renewal inspection where the utility had to drain and inspect their diesel oil tanks due to an EPA requirement.

Patricia Lougheed

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[chicopee]

Fuel oi tanks are prone to moisture contamination unlike propane whereby methanol will be added to cope with moisture.

 

[unclesyd]

We had around 10 Propane bullets tanks that were on a five year internal inspection interval which has recently been changed to a 10 yr schedule with UT on a 4 yr schedule.
Originally these tanks were used for Butane service until the industry changed to Propane. If I recall correctly the bullets were on a 3 yr internal inspection. During the Butane years there was some corrosion found. The Butane industry had a propensity to allow a little water into their storage systems as water was cheaper than Butane.

I don't know about the commercial aspects of the Propane business but on the consumer end there are still some water problems. I just recently had to have a 100 gal Propane tank refurbished and repainted and during this process it was found that there were approximately five gallons of water in the tank. I had the thickness checked and all were in limits.

 

[ApC2Kp]

unclesyd,

One aspect of the propane business that gives pause to the materials guys is the dual purpose loads of the road transport tankers. These over-the-road tanks haul propane and then haul ammonia in alternating seasons to the agricultural market. I have wondered what decontamination procedures are taken at change-over. The washout of the ammonia heel with water might be the source of water in user propane tanks. Freeze up of propane lines and regulators is one hassle not needed in winter conditions. The brass and copper fittings of propane piping must be in annealled condition to avoid the ammonia stress cracking that could occur.

The propane storage bulllet tanks would be ASME code stamped. Not all states (Texas?) require ASME stamped tanks. The required inspection intervals are usually set by state agency, and users set more frequent intervals as needed, or as the plant insurers require.

 

[unclesyd]

Though we are not a code state either all our bullets were ASME stamped based on corporate policy. We initially used the inspection schedule for the tanks based on one of our parent companies based on their operation in a Code state.


Anecdotal:

We experienced first hand the cross contamination between trucks hauling Propane and Ammonia. We had to take our two Ammonia storage Horten Spheres out of service due to a cracking problem. Instead of our normal barge delivery of Ammonia we set up to receive trucks. Our purchasing specifications specifically called for trucks that had only been used for Ammonia service. Our outage lasted longer than first anticipated and we had to triple the amount of truck deliveries. As soon as we increased the delivery rate we started noticing a decrease in our catalyst activity in our process of hydrogenating Adiponitrile(ADN). It got bad very quickly and as we were beginning to investigate some field operators started reporting that our hydrogenation product smell like gasoline. While inspecting the unloading operation to set setup a sampling station I mentioned to the group that some of the trucks were really pretty and clean. My boss quickly got some ADN on a rag and started to wipe the area where the sign stated "Anhydrous Ammonia Only". As the fresh paint was removed the sign changed to Propane. The villain in the lost of catalyst activity was the Mercaptans used to odorize the Propane. Our losses were in excess of $1,000,000 dollars. Our biggest loss was with the Cobalt catalyst because our regeneration system couldn't remove the sulfides. The trucking company went out business the day after we discovered the deception.

 

[JohnBreen]

It really depends upon the jurisdiction and the laws and regulations in place in the particular state, commonwealth or province. Generally the mandated inspection interval is periodic with no adjustment for documented rate of corrosion

We have had some success in convincing our Commonwealth that refrigerated, insulated, LPG VESSELS that store product at -40 C do not need to be inspected every ten years. There is obviously some little risk in emptying the vessel (and so doing arrive at the most combustible air/fuel ratio) and then refilling. Not to mention the damage to the frozen insulation that occurs when the VESSELS are taken out of service and brought up to ambient temperature. "Hot" bullets (VESSELS) are simply going to have to be inspected periodically until the laws and regulations are updated to include the API 579 approach.

There is a LOT of (many years) experience from the refrigerated ammonia service that can provide convincing statistics on corrosion rates for refrigerated carbon steel VESSELS. Sometimes you have to just get your ducks in a row (prepare a convincing argument based upon the facts) and go and discuss the pros and cons with the (hopefully receptive) jurisdiction.

 

[unclesyd]

JohnBreen,
One has to be careful when using the history of a vessel in a particular service based on experience as there may be problems that haven't been recognized. We were fat and happy with our two Horton Spheres, Anhydrous Ammonia Storage, based on other people experience as well as our prior use of bullets. We heard through the grape vine, actually a conversation between two NDT technicians that some problems had been found in a Sphere. Based on this we started inspecting ours and found the oldest to be full of cracks. Then we opened the newest and found it was all cracks. The MOC was different, the oldest was a lower strength material than the newest one.
As we started looking at our Ammonia Recovery System we discovered that we also had problems with our Aqua Ammonia Storage tanks, Hydrogen blistering to the point that we had to replace the bottom ring in two tanks. Fortunately we had no problems with our four Ammonia Recovery Columns.

The same was true with our 3 DA's. We were happy until we started inspecting them. We had just inspected one and were conferring with AI about the cracking we found when one of the first reported failures, with a fatality, occurred.

We were also complacent with our PSA Hydrogen Purification System based on our and other's experience, that is until we had a leak in a long seam of one vessel. We repaired the leak and other cracks and opened another one that also had cracking to a lesser degree. The tanks were on a twenty year internal inspection with a ten year UT inspection.